Yonisomanasikara means wise reflection. Sati-Sampajano, in general terms, means Clear Comprehension. Sati means mindfulness, Sampajano makes Sati a bit bigger. Sati by itself is just being mindful of what is. That is just Sati by itself, being mindful of what is. Sati-Sampajano is bigger. Sati-Sampajano is mindfulness of what is and clearly comprehending not only what is, but also what is going to be the result.
A typical little example that I like to use: I want to practice Sati. I'm going to try to be very mindful of my arm. I am going to raise my arm in the air and I am going to feel every muscle in my arm, in my shoulder, even in my side. I can feel my arm, I can feel my muscles very clearly and I move my arm to the right. I am practicing Sati very clearly and my mind focuses on my arm. That is Sati. Now if somebody is sitting next to me on my right, I just hit them in the face. No Sati-Sampajano.
Now, I am going to practice Sati again, but I am also going to practice Sati-Sampajano. I am raising my arm up and I am feeling my muscles, I raise it all the way up to the top and now I decide I am going to move it and Sati-Sampajano comes in right now, I think, "Should I move it to the right or should I move it to the left?" To the left, no problem, to the right, "Oh, somebody is sitting there. I'd better move it to my left." So then I go back practicing Sati by moving my hand to my left. Fine.
That is Sati-Sampajano, it is clearly comprehending what is and the results. Yonisomanasikara includes Sati-Sampajano. They are not the same thing, but Yonisomanasikara includes it, it is all wise reflection, the whole works. Any kind of wise reflection is part of Yonisomanasikara. Sati-Sampajano is a specific type of wise reflection, observing this moment and understanding the results of this moment, the possible outcome. So in that way Sati-Sampajano or Clear Comprehension is a subgroup of Yonisomanasikara. Any kind of wise reflection is Yonisomanasikara, and Sati-Sampajano is part of it.